The high neutron flux of Californium-252, with its relatively high neutron/gamma ratio, low oxygen enhancement ratio, higher linear energy transfer, greater relative biological effectiveness, and the small quantities of isotope required, makes it desirable as a more effective radiotherapeutic isotope than are Ra-226, Cs-137, or Co-60. A gap exists between cell culture studies and the clinical usage of Cf-252 under physiological conditions. We propose to use miniature swine as an experimental animal in the study of the response of normal tissue to intracavitary cervical implantation of Cf-252. Extensive dosimetric studies will include theoretical calculations, phantom dosimetry, and, where possible, in vivo dosimetry. Radiobiological responses to Californium-252 will be compared to those resulting from Ra-226.